mug vs mugger

mug and mugger both are nouns.

Word	Noun	Adjective	Verb	Adverb
mug	Yes	No	Yes	No
mugger	Yes	No	No	No

mug (noun)	mugger (noun)
with handle and usually cylindrical	a robber who takes property by threatening or performing violence on the person who is robbed (usually on the street)
the human face (`kisser' and `smiler' and `mug' are informal terms for `face' and `phiz' is British)
a person who is gullible and easy to take advantage of
the quantity that can be held in a mug

mug (verb)	mugger (verb)
To stare awkwardly
rob at gunpoint or with the threat of violence